FIG. 28 is a schematic top view of conventional acoustic wave element 501 disclosed in PTL 1. Acoustic wave element 501 includes piezoelectric substrate 502, excitation electrode 503, and receiving electrode 504 formed on piezoelectric substrate 502, dielectric layer 506 formed on piezoelectric substrate 502 for covering excitation electrode 503 and receiving electrode 504, sensing portion 505, and a detector. Sensing portion 505 is formed on piezoelectric substrate 502 and above a propagation path of main acoustic wave 507 between excitation electrode 503 and the receiving electrode 504. The detector detects characteristics of main acoustic wave 507 excited by excitation electrode 503.
Characteristics, such as a frequency and a phase, of main acoustic wave 507 change upon sensing portion 505 contacting a test substance, such as expired air or test liquid, that may possibly contain an object substance. The detector detects the change in the characteristics, and senses, e.g. a presence or a concentration of the object substance.
Conventional acoustic wave element 501 may not ensure sensitivity of sensing portion 505.